Many current engines manufactured by auto makers use aluminum cylinder heads for a number of reasons, including weight reduction for the engine. Currently, these aluminum cylinder heads are fitted with iron base valve guides and valve seats to provide necessary wear and heat resistance and also desired sealing with the commonly used poppet-type valves. The poppet-type valves have an elongated stem portion with a circular cross-section and an enlarged head portion attached to the stem portion. The valves cannot operate directly in an aluminum head in contact with the aluminum because of the softness of the aluminum material and its low melting point.
In utilizing iron base valve guides and valve seats in an aluminum or other metal type head, the hole for the valve guide which supports the valve stem is very accurately drilled and machined so as to be coaxial with the circular valve seating portion formed by the separate valve seat member. In this regard, the valve seat member is normally of hardened iron base material and when attached to the cylinder head, it is first cooled as by insertion in liquid nitrogen and then inserted into the cylinder head. Subsequently, the valve seat must be finish machined on its inside diameter to ensure accurate coaxial alignment with the valve stem supporting hole in the guide and to ensure good sealing with the head of the poppet-type valve. This is the process by which valve guides and seat portions are assembled and finished in all engines known to applicant.
It has been known previously to cast valve guide or valve seat components within a cylinder head. The U.S. Pat. No. 4,570,585 to Hayashi shows a sheet metal formed valve seat which is embedded in the block or cylinder head by casting the cylinder head around the valve seat insert. It has also been known to form an integral valve seat and stem guide for valving in internal combustion engines. The U.S. Pat. No. 4,008,695 to Bouquet discloses a one-piece metal valve seat and stem guide structure with integral cooling chambers therein. This type of device, called a valve chest in the patent, is known to have been used in diesel engine construction.
It has also been known to use ceramic materials for components in an internal combustion type engine. In U.S. Pat. No. 4,494,500 to Hansen, a rotary sleeve type seal of ceramic material is disclosed. This structure is quite dissimilar to the normal poppet-type valving arrangement for internal combustion engines.